A tearing-strength test apparatus known as the USTER TENSO JET (USTER being a registered trademark of Zellweger Uster AG) provides an example of a type of yarn tester which is of interest. This is described in EP-A-403,988 and its U.S. counterpart Pat. No. 5,050,437. In such a tester the stretching of the test material is carried out by two rotating pairs of rollers which are spaced from one another and between the rollers of which is formed a periodically opening and closing nip for the test material. This test apparatus is characterized by, among other things, a very high testing speed which, particularly in the testing of yarn from different bobbins, requires a corresponding insertion mechanism for the threads to be tested.
The cited EP-A-403,988 and its U.S. counterpart Pat. No. 5,050,437 mention and illustrate as a suitable insertion mechanism the mechanism which is known from the USTER TENSORAPID and which contains an insertion arm for the thread. This insertion arm is described in principle in U.S. Pat. No. 4,319,493. It is mounted in a link which is guided in a rail oriented vertically in the thread running direction, so that, during each insertion cycle, the head of the arm follows a path along a closed, approximately rectangular curve. The arm carries on its head a controlled thread clamp which grasps the thread, inserts it into the test apparatus and releases it after it has been taken over by the latter.
Practical tests have shown that this insertion mechanism works relatively slowly and the testing speed is consequently limited. The arm follows a relatively complicated path during the insertion of the thread, and during each insertion cycle, the thread clamp arranged on the arm has to be activated twice. Moreover, the transfer of the thread, drawn out by the insertion arm at its head part, to the take-over member is also relatively complicated and necessitates an exact positioning and synchronization between the take-over member and the thread clamp of the insertion arm. This known insertion mechanism also takes up a relatively large amount of space, giving rise not only to a cumbersome appearance but also to excess costs.